We visited this campsite last year on our way to and from the Vendee, we only satayed 1 night each ime and we were in a Canvas caravan, so I can't comment on the washing facilities etc.
The site is good, with lots of facilities. The swimming pool area is excellent, with a little 'lazy river' and slides. There is a covered pool (top can also be opened up) if the weather is poor. There is a good play park, with IIRC a sand base.
The camp site is a fair drive from Caen but was eay to find, took us about 15-20 minutes iirc, so a taxi would be quite expensive. We walked to the beach, it is a good 30 minute walk, longer if the kids are tired. The local village is a nice seaside town, I can't comment of the shops as we didn't stay that long. There is a reasonable shop on site, but I would use that for things like bread and mild etc, as it is a bit more expensive than the supermarkets and has less choice.
The site also has a bar. It wasn't too noisy at night but is 'busy. It is a big site and I wouldn't be happy about my kids going to the park also (something we like to do on small site)
Re the car thing. You will be quite 'tied' to St Aubin if you don't have a car and you might be putting a lot of trust inthe Normandy weather. It tends to be just a bit better than the UK, but can be changable.
HTH